Hume's Fork and Psychiatry's Explanations: Determinism and the Dimensions of Freedom

These items piqued my interest not merely because they play into the public's worst stereotypes concerning psychiatric diagnosis—"You shrinks think every kind of bad behavior is a disease!"—but also because they raise the most fundamental questions concerning freedom, responsibility, and mental illness. Since the vexing question of "free will" has been debated by theologians and philosophers for centuries, with neuroscientists weighing in more recently, I do not propose to resolve this matter in the space of one column (even medical editors are not that grandiose). I do hope to present an overview of the philosophical issues as they impinge on psychiatric theory and practice, and to put forward a conceptual schema for understanding how persons may have a mental illness and yet be responsible in some measure for their actions.

However, to accomplish the latter, I first need to put forth a somewhat unfamiliar, if not unwelcome, concept of what it means to act using free will. Informulating my position, I am indebted to the work of philosophers Moritz Schlick, Thomas W. Clark,³ Owen Flanagan,⁴ and Daniel C. Dennett,⁵ among many others.

Let's begin by considering a paradox known in philosophical circles as "Hume's fork," ostensibly derived from the work of the great Scottish philosopher David Hume.⁶ The paradox goes something like this: Either all our actions are determined, in which case we are not responsible for them; or, our actions are the result of random events, in which case we are still not responsible for them!

To understand the first part of this dilemma, we briefly need to consider the concept of determinism. In its most basic formulation, determinism simply asserts that everything that happens is caused, and that when an event occurs, nothing other than that event could have occurred at that particular moment given precisely the same conditions immediately preceding the event. Determinism is not to be confused with fatalism or predestination, both of which imply that no matter what we do, the future will turn out in one and only one way. Determinism asserts, on the contrary, that our actions are crucial in shaping the future.

Keeping this in mind, we can see that the first part of Hume's dilemma might imply nothing less than this: If all our wishes, desires, and actions are merely the inevitable result of innumerable causal factors coalescing since the beginning of time, we cannot possibly have free will or reasonably be held morally accountable for our actions. (Thomas Aquinas appreciated these implications more than 7 centuries ago.)

You can easily imagine how this argument, applied to the subset of persons who have serious psychiatric disorders, becomes even more destructive to our commonly held notions regarding freedom and responsibility. If everyone's actions are merely the result of a chain of causation extending back ad infinitum, how much less free will must someone with schizophrenia have? He or she, after all, carries the added "causal burden" of brain pathology based on the best available science. And how could we possibly argue that such brain-impaired persons should be held accountable in any way for their actions? With this view, surely, our "Internet addict" (whatever that means) might just have a case in denying any culpability for his on-the-job behavior.

And alas, the other "tine" in Hume's fork does not help us much either if we are intent on salvaging our ordinary concept of personal responsibility. If our actions do not proceed from an unbroken chain of causal events; if, on the contrary, our behavior is the product of random factors operating beyond the realm of causality, then we are clearly not the authors of our actions in any meaningful sense. By the way, the quantum mechanics loophole—the hypothesis that strict determinism may not hold at the level of subatomic particles—does not do us much good, because the molecular and electrochemical events in the brain occur on a scale many magnitudes larger than that of Heisenberg's wave-particle uncertainty principle.

Philosophers, ethicists, and theologians have proposed several ways out of Hume's dilemma, and it is beyond the scope of this brief piece to review them.^4,6,7 However, I would like to defend the position taken prominently by the German philosopher Moritz Schlick that determinism and causal law do not vitiate free will or moral responsibility. On the contrary, Schlick argued that our ability to act with genuine freedom depends on causality and determinism.⁷ Schlick pointed out that causal laws are not proscriptive in the way that civil laws are; rather, they are descriptive and merely tell us how the physical world actually functions. The view that determinism and free will are compatible is sometimes termed "compatibilism" or, in more recent versions, "neo-compatibilism."⁴ Of course, Schlick's position rests on the admittedly controversial hypothesis that determinism invariably operates throughout the universe—and thus, in the sphere of our own thoughts, feelings, and actions.

Essentially, the compatibilist argument is that we cannot be free or responsible beings if our actions are mysteriously chosen by an entity that somehow slips the surly bonds of causal law and acts independently of our goals, values, and wishes. On the contrary, whether we call that volitional entity "will," "soul," "psyche," or "I," it must be causally linked with our core values to effect morally responsible actions. That is, to preserve free will, the "state of my will (itself determined by prior and contemporaneous causes) must be a sufficient cause of any choice I make."⁴

Indeed, I would like to suggest that the tighter the causal links between our decision-making capacity and our innermost values, the freer and more responsible are the decisions that we make.